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United States Patent |
5,001,679
|
Harrison
|
March 19, 1991
|
Dual shuttle air gun
Abstract
A dual shuttle air gun for generating maximum acoustic output for seismic
testing having a housing with an air chamber formed therein and a chamber
opening that opens 360 degrees around the periphery of the body is
disclosed. The two shuttles are positioned around the housing axially
displaced from each other, but close enough to allow the end faces of each
shuttle to come into close proximity with each other. When the air gun is
fired by the activation of a solenoid, compressed air flows into a firing
chamber formed between the first shuttle and the housing causing the first
shuttle to begin opening. When the first shuttle moves, the end faces of
the two shuttles are exposed to the compressed air from the primary
chamber. This causes the two shuttles to rapidly move away from each other
providing for very quick release of the stored compressed air. When the
solenoid is deactivated, the two shuttles are forced back into a prefire
condition over the 360 degree opening.
Inventors:
|
Harrison; Earnest R. (Plano, TX)
|
Assignee:
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Halliburton Geophysical Services, Inc. (Houston, TX)
|
Appl. No.:
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472197 |
Filed:
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January 30, 1990 |
Current U.S. Class: |
367/144; 181/120 |
Intern'l Class: |
H04R 023/00 |
Field of Search: |
367/144
181/120
|
References Cited
U.S. Patent Documents
4364446 | Dec., 1982 | Thomas et al. | 367/144.
|
4623033 | Nov., 1986 | Harrison, Jr. | 367/144.
|
Primary Examiner: Jordan; Charles T.
Assistant Examiner: Eldred; J. Woodrow
Attorney, Agent or Firm: Arnold, White & Durkee
Claims
What is claimed is:
1. An air gun responsive to a supply of compressed air, comprising:
a housing assembly defining a chamber and a discharge port through which
said chamber may be communicated with the environment surrounding the air
gun;
a first valve means movably arranged relative to said housing for at least
partially closing said discharge port in a first, closed, position, and
for opening said discharge port in a second, open, position;
a second valve means movably arranged relative to said housing for at least
partially closing said discharge port in a first, closed, position, and
for opening said discharge port in a second, open position, said first and
second valve means being movable generally simultaneously and in generally
opposed directions to open said discharge port; and
means for selectively actuating said air gun to move said first and second
valve means from their respective first positions to their respective
second positions.
2. The dual shuttle air gun of claim 1 wherein said first valve means
comprises a first shuttle disposed generally coaxially with said housing,
and slidable between said first and second positions.
3. The dual shuttle air gun of claim 2 wherein said second valve means
comprises a second shuttle disposed generally coaxially with said housing,
and slidable between said first and second positions.
4. An air gun adapted to be coupled to a compressed air source, said air
gun comprising:
a housing assembly defining a primary chamber, and a port for communicating
said chamber with the environment exterior to said air gun housing;
a first shuttle slidably disposed around said housing, said shuttle
moveable between a first position at least partially covering said
discharge port and a second position essentially uncovering said discharge
port, said first shuttle and said housing assembly cooperatively
substantially defining a first control chamber;
a second shuttle slidably disposed around said housing assembly, said
second shuttle moveable between a first position at least partially
covering said discharge port, and a second position essentially uncovering
said discharge port, said second shuttle and said housing cooperatively
defining a second control chamber, said first and second valve means both
being in their respective first positions to cover said discharge port;
means for supplying compressed air to said primary chamber in said housing
assembly, and to said first control chamber formed by said first shuttle
and said housing assembly, and to said second control chamber formed by
said second shuttle and said housing assembly; and
means for actuating said air gun.
5. An air gun adapted to be coupled to a compressed air source, said air
gun comprising:
a housing assembly defining a primary chamber, and a port for communicating
said chamber with the environment exterior to said air gun housing;
a first shuttle slidably disposed around said housing, said shuttle
moveable between a first position at least partially covering said
discharge port, and a second position essentially uncovering said
discharge port, said first shuttle and said housing assembly cooperatively
substantially defining a first control chamber;
a second shuttle slidably disposed around said housing assembly, said
second shuttle moveable between a first position at least partially
covering said discharge port, and a second position essentially uncovering
said discharge port, said second shuttle and said housing cooperatively
defining a second control chamber, wherein one of said first and second
shuttles includes a lip which cooperates with the other of said shuttles
to allow a chamber to be formed between said shuttles after movement of
either of said first and second shuttles;
means for supplying compressed air to said primary chamber in said housing
assembly, and to said first chamber formed by said first shuttle and said
housing assembly, and to said second chamber formed by said second shuttle
and said housing assembly; and means for actuating said air gun.
6. The air gun of claim 4, wherein said actuating means comprises a
solenoid cooperatively arranged with air passages in said air gun.
7. The air gun of claim 6, wherein said solenoid is adapted upon actuation
to communicate compressed air to said second chamber cooperatively formed
by said first shuttle and said housing assembly.
8. The air gun of claim 4, wherein said discharge port extends essentially
360.degree. around said housing assembly.
9. An air gun responsive to a supply of compressed air and an electrical
signal, comprising:
a housing assembly adapted to be coupled to said supply of compressed air,
said housing assembly having a primary chamber and a discharge opening
therein extending 360.degree. around the periphery of said housing
assembly, said chamber adapted to receive and store the compressed air;
a first valve member slidably mounted around said housing;
a second valve member slidably mounted around said housing, whereby said
first and second valve member coact to block said discharge opening to
maintain the compressed air in said primary chamber when in a prefire
position;
a solenoid operatively coupled to said housing, said solenoid connected to
receive the electrical signal and to be activated thereby;
a firing chamber formed between surfaces of said housing and said first
valve means, said firing chamber connected to receive compressed air when
said solenoid is activated.
10. The apparatus of claim 9 wherein the first and second valve means
comprise respectively first and second sleeve shuttles which encircle said
housing.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a high pressure air gun for the generation of
seismic energy in water, and more particularly to a high pressure air gun
employing a dual sleeve-type shuttle allowing optimized air discharge and
acoustic pressure pulse within the shortest possible time.
2. Description of the Prior Art
In marine seismic exploration, a source of acoustic energy is released into
the water every few seconds to produce appropriate acoustic waves that
propagate from the source into the earth's surface. These acoustic waves,
upon contacting the marine floor and subfloor geologic formations, are
reflected back to recording instruments having transducers which convert
these waves into electrical signals which are then recorded. Analysis of
these electronic signals provides insight into the structure of the
subsurface geological formations.
There have been many devices utilized for generating these seismic or
acoustic waves. Most recently, however, a major marine seismic energy
source has been the air gun. (The term "air gun" is intended to encompass
an apparatus for dispersing any suitable compressible gaseous fluid such
as air, steam, nitrogen, carbon dioxide, gaseous products of combustion
and so forth.) These air guns are capable of releasing high pressure air
on the order of 2,000 psi to 6,000 psi in the water to create the desired
acoustic waves.
The acoustic pulse generated by an air gun is proportional to the bubble
velocity formed by the air escaping the air gun. As the air exits the gun
ports a bubble is formed. This bubble accelerates outwardly generating the
acoustic pressure pulse which creates the seismic wave. As long as the air
bubble/water interface is accelerating, the acoustic pulse amplitude is
increasing. Once the maximum bubble velocity is reached, then the maximum
acoustic pulse is achieved.
Conventional air guns typically include an annular housing having a chamber
in which compressed air is stored, and exhaust ports which allow the
stored air to escape from the housing. The only moving component of the
air gun, except for a solenoid triggering device, is a shuttle valve
which, when shifted, permits air to escape from the firing chamber through
the exhaust ports in the main housing into the surrounding water. The guns
also include a constant source of compressed air through an inlet passage
in the housing which supplies the compressed air for the storage chamber
and which enters a control chamber to force the shuttle into a closed
position over the exhaust ports in the housing. A solenoid valve is used
to allow air to flow into a firing chamber opposite the control chamber
having a shuttle bearing surface of greater surface area than the bearing
surface in the control chamber. This creates unequal pressure on the
shuttle, forcing the shuttle in an open position to expose the exhaust
ports and allow the compressed air to escape into the surrounding water.
When the shuttle is in a prefire or closed position, the air gun is
charged and ready for firing. When fired, by activating the solenoid, the
compressed air escapes into the water.
A particular air gun of this type is described in Chelminski U.S. Pat. No.
4,472,794. This air gun comprises a housing and a primary chamber within
the housing and a movable shuttle control adapted to reciprocate along an
annular chamber within the housing between a first position covering
exhaust ports in the primary chamber and a second position laterally
displaced from the exhaust ports to allow air to escape from the primary
chamber.
A constant source of compressed air is supplied to the air gun which
initially acts to force the shuttle into the first position blocking the
exit of air through the exhaust ports. This is accomplished by compressed
air acting against an exposed upper end surface area of the shuttle within
the annular chamber. The same compressed air source also supplies
pressurized air into a primary chamber and builds the pressure to a
predetermined level. A solenoid controlling the flow of compressed air is
activated which then causes compressed air to bear against a surface on an
exposed lower end of the shuttle creating a pressure differential which
causes the shuttle to shift, exposing the exhaust ports. As the shuttle
begins to shift the shuttle's entire lower end surface area is exposed to
the pressurized air in the primary chamber. This produces a high
acceleration opening force, rapidly shifting the shuttle to fully expose
the exhaust ports.
In the Chelminski air gun, however, the exhaust area is much smaller than
the 360.degree. periphery of the housing. In addition, because the
compressed air in the storage chamber fills a volume equaling the entire
space within the storage chamber, the overall average path length for the
pressurized gas in discharging from the firing chamber through the exhaust
ports is greater than would be desired. Furthermore, once the shuttle is
released, there is no further control of the shuttle. The shuttle can
return to its prefire condition only by virtue of the air in the firing
chamber dropping to some predetermined level.
The inventor of the present invention solved many of the problems
associated with the Chelminski invention and other prior art in his U.S.
Pat. No. 4,623,033. The air gun of that invention includes an annular
housing having a primary chamber for storing compressed air where the
primary chamber opens 360.degree. around the periphery of the housing,
surrounding a center post section of the body. An external sleeve-type
shuttle surrounds the body and is movable between a first position
covering the 360.degree. opening in a prefire mode and a second position
exposing the 360.degree. opening in a fired position. The single shuttle
is held in the prefire or first position by pressure from a source of
compressed air acting against a bearing surface of the shuttle in a
control chamber formed within the body. This source of compressed air also
supplies the air for the primary chamber. The shuttle is forced into the
second or fired position by a solenoid activated by an electrical signal
which causes compressed air to flow into a firing chamber. The resultant
force in the firing chamber becomes larger than the holding force of the
control chamber, thereby causing the shuttle to abruptly slide along the
outside surface of the housing suddenly and continuously opening the
360.degree. port of the primary chamber. Compressed air from the primary
chamber is thus released suddenly into the surrounding water.
When the solenoid is deactivated, by removing the electrical signal, the
shuttle is then able to move back into the prefire or first position under
the influence of the pressure from the control chamber, which pressure is
supplied by the continuous supply of compressed air feeding both the
control chamber and the primary chamber. In this manner the movement of
the shuttle is completely controlled by the solenoid.
A limitation on the performance of conventional air guns is believed to be
the rate at which the flow area for the escaping air may be increased. In
conventional air guns, as described earlier herein, the rate of the flow
area increase is limited by its smaller port size and the rate at which
the air gun shuttle may move. Accordingly, the present invention provides
a new method and apparatus which uses multiple shuttles to optimize the
rate of opening of the flow area to thereby optimize the rate of discharge
of the air.
SUMMARY OF THE INVENTION
The present invention provides for maximum bubble velocity by allowing for
a maximum discharge of stored compressed air from a primary chamber into
the surrounding water. This rapid discharge is made possible by the
addition of a second movable sleeve shuttle which is employed to more
rapidly uncover the 360.degree. annular port when the air gun is fired.
The external sleeves' operation permits the 360.degree. exhaust flow area
to increase as the sleeves move apart in response to air pressure
differentials acting on opposite surfaces of the shuttles. The air exhaust
flow area is limited only by the combined stroke distance of the two
shuttles. This combined action produces a very large acoustic output. This
second valve more than doubles the rate of increase in flow area, as
compared to conventional air guns.
The air gun of the present invention includes, in a particularly preferred
embodiment, an annular housing which in turn has formed within it a
primary chamber for storing compressed air. The primary chamber opens
360.degree. around the periphery of the housing surrounding a center post
section of the body. A first external sleeve-type shuttle surrounds the
body and partially covers the 360.degree. opening. A second external
sleeve-type shuttle also surrounds the body and comes to near contact with
the face of the first shuttle to completely cover the 360.degree. opening
in a prefire position. The dual shuttles are held in this prefire position
by pressure supplied from two control chambers formed between the body and
the sleeve shuttles and which bear against surfaces of the shuttles. The
air pressure is supplied by a continuous source of compressed air.
In this particularly preferred embodiment, the air gun includes a first
control chamber formed in a space between the gun housing, the inner
surface of the first sleeve shuttle and an inwardly extending lip of the
first sleeve shuttle. Compressed air bears against the exposed surface
area of the lip forcing the shuttle away from the air source. Air is
supplied to this first control chamber by a common source of compressed
air which supplies both this first control chamber and the primary chamber
of stored compressed air. A second control chamber is formed in a space
between the gun housing, the inner surface of the second sleeve shuttle
and an inwardly extending lip of the second sleeve shuttle. Compressed air
from the primary chamber enters this control chamber and bears against the
exposed surface area of the lip tending to force the second sleeve shuttle
to the left to come into close proximity with the face of the first sleeve
shuttle.
In the operation of this particularly preferred embodiment, when a solenoid
is activated by an electrical signal, compressed air is permitted to flow
into a firing chamber formed between the body of the housing and an
opposite exposed surface area of the lip of the first sleeve shuttle; this
surface being larger than the lip surface in the control chamber of the
first sleeve shuttle. The pressures acting against the first sleeve
shuttle in both the control chamber and the firing chamber create a
resultant force in the firing chamber larger than the holding force of the
control chamber, thereby causing the first sleeve shuttle to abruptly
slide along the outside surface of the housing to begin opening the
360.degree. port of the primarY chamber. As soon as the face of the first
sleeve shuttle is separated from flush contact with the chamber face seal,
compressed air from the primary chamber is allowed to act on the faces of
both the first and second sleeve shuttle causing them to rapidly slide in
opposite directions and away from the discharge ports. This dual shuttle
movement more rapidly opens the discharge flow area to allow a more rapid
escape of the compressed air from the primary chamber.
The center support structure required for the 360.degree. port forces the
pressurized air in the primary chamber closer to the 360.degree. port
providing a greatly reduced average path length for the compressed air,
further aiding a more rapid discharge.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a seismic energy source air gun in accordance with the
present invention, depicted in vertical section.
FIG. 2 schematically depicts the air gun of FIG. 1 in vertical section
along line 2--2 in FIG. 1.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to FIG. 1, therein is depicted an air gun 10 in accordance
with the present invention. The air gun 10 includes a housing 12
cooperatively defining a generally annular primary chamber 14 around a
center post mandrel 16. A first sleeve shuttle 18 is concentric to housing
12 and includes an inwardly protruding lip 20 extending from approximately
the mid portion of first sleeve shuttle 18 toward center post mandrel 16.
An end cap 15 is threadably attached to center post mandrel 16, and forms
an extension of mandrel 16. First sleeve shuttle 18 has a shuttle face 22
at a first end, proximate a first end of housing -2. A second annular
shuttle 24 is provided which encircles housing 12. Second shuttle includes
a lip 26 which extends from a shuttle face 28 overlapping face 22 of
shuttle 18. Housing 12 and mandrel 16 define an openable 360.degree. port
27 communicating chamber 14 with the exterior of air gun 10. Face 22 of
shuttle 18 closes port 27 when air gun 10 is in a prefire position.
An annular control chamber 30 is formed between housing 12 and shuttle 18,
bounded also by lip 20. A firing chamber 32 is formed on the opposite side
of lip 20 between shuttle 18 and body 12. A vent 38 in shuttle 18 provides
venting for the firing chamber 32. A second control chamber 40 is formed
between shuttle 24 and housing 12 bounded also by lip 26 on shuttle 24. A
port 42 communicates second control chamber 40 with primary chamber 14 to
provide a source of compressed air to act against a surface of shuttle 24.
Seals 47, 48, and 49 are appropriately placed to seal between shuttle 18
and mandrel 16 to define chambers 30 and 32. Similarly, seals 50 and 51
are appropriately arranged between second shuttle 24 and housing 12 to
sealingly define chamber 40. Seals 47, 48, 49, 50, and 51 may be of
conventional types as known to the art.
Solenoid 52 is shown attached to end cap 15. End cap 15 includes an air
inlet 54 communicating with a first air passageway 56. Air passageway 56
is connected to control chamber 30 through a passageway 64 (depicted in
dashed lines), and to primary chamber -4 through passageway 68 (also
depicted in dashed lines).
In operation, air gun 10 functions as follows: Pressurized source air
enters air gun 10 through an inlet 54 and traverses passageway 56 both to
control chamber 30 and primary chamber 14. The pressure in control chamber
30 acts against the exposed surface formed by lip 20 in shuttle 18 forcing
shuttle 18 to move until its face securely contacts main seal 70 in
housing 12, moving shuttle 18 to the right as depicted in FIG. 1. As air
pressure in primary chamber 14 increases, air flows into control chamber
40 through orifice 42 and acts on the exposed face of lip 46 of shuttle
24. This pressure forces shuttle 24 securely against shoulder 100, and
close to the adjacent face of shuttle 18 (i.e., moving shuttle 24 to the
left as depicted in FIG. 1). Once primary chamber 14 is fully pressurized,
air gun -0 is ready to fire.
Air gun 10 is fired by applying an electrical current to the solenoid valve
52 to actuate the valve and allow source air to flow into actuation
passageway 60, and into firing chamber 32. This pressure acts on shuttle
18 provides a force urging the shuttle 18 against the spring force in
chamber 30. Because face 34 of shuttle 18 is larger than the exposed
surface of lip 20 within control chamber 30, a bias is created causing
shuttle -8 to move in an opening direction (to the left, as depicted in
FIG. 1). As shuttle 18 moves away from face seal 70 on body member 12, the
primary chamber air flows outward into the cavity formed between shuttle
-8 and the overlapping lip 26 of shuttle 24. This high pressure air from
primary chamber 14 acts against face 22 of shuttle -8 and face 28 of
shuttle 24 forcing the dual shuttles to move rapidly away from each other.
This opening force continues until outside diameter of shuttle 18 clears
the lip 26 of shuttle 24 at which time the primary chamber air starts to
exhaust into the surrounding water through the 360.degree. port opened by
the movements of the two shuttles.
If solenoid 52 is kept activated, then the high pressure remains present in
passageway 60. With shuttle 18 moved to the left, firing chamber 32 tends
to exhaust air through vent 38. Shuttle 18 then tends to move to the right
because of the pressure in control chamber 30 but is immediately moved
back to the left by the pressure in firing chamber 32. This results in an
oscillatory motion until solenoid 52 is deactivated. When solenoid 52 is
deactivated, the pressure in passageway 60 is removed and the spring force
in chamber 30 moves shuttle 18 to the right, back to the prefire position
as described above. When face 22 of shuttle 18 comes into contact again
with face seal 70, pressurized air from passageway 68 entering into
primary chamber 14 causes pressure to build up in the primary chamber, and
also to enter control chamber 40, to thereby move shuttle 24 securely
against shoulder 100. Lip 26 of shuttle 24 then overlaps face 22 of
shuttle 18 completing the prefire orientation of the dual shuttle air gun
Many modifications and variations may be made in the techniques and
structures described and illustrated herein without departing from the
spirit and scope of the present invention. Accordingly, the embodiments
described and illustrated herein are illustrative only and are not
intended as limitations upon the scope of the present invention.
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